Engines include a plurality of cylinders having combustion chambers with pistons disposed in the combustion chambers. Intake air is directed into the combustion chambers by air handling systems of the engines and is compressed in the combustion chambers. Fuel is injected into the combustion chambers at a fuel injection time and is ignited. The ignited fuel generates pressure in the combustion chamber that moves the piston. The ignition of the fuel creates gaseous exhaust in the combustion chambers that is at least partially carried out of the engine by the air handling systems.
Emission standards have been created to reduce pollutions from emissions into the environment. One of these standards is referred to as the Tier 4 emission standard. Manufacturers have utilized a dual-fuel engine that injects a combination of diesel fuel and natural gas into the combustions chamber for ignition. In particular, by substituting natural gas in for diesel, less diesel fuel is used improving emissions.
While emissions are improved, problems remain. Specifically, natural gas, a diesel fuel substitute in a dual-fuel engine, is combustible. With a diesel engine, the air in the combustion chamber is compressed to increase the temperature of the air within the combustion chamber to such a temperature that upon introduction of the diesel fuel ignition occurs without the need of an external spark. Thus, diesel engines are extremely efficient and high compression ratios within the cylinder are desired. Because the diesel fuel is the catalyst for ignition, injection of natural gas into the combustion chamber must occur prior to injecting the diesel fuel. This is problematic because the natural gas can ignite before the diesel fuel is added at high enough pre-combustion temperatures within the combustion chamber. This is referred to as knocking, which can cause catastrophic failure to the engine.